In general, soybean, which is one of the pulse crops, contains isoflavone compounds including daidzin, daidzein, genistin and genistein.
The isoflavone compounds are represented by the following formula and Denotative Table. ##STR1##
Denotative Table R1 R2 daidzin H glucose daidzein H H genistin OH glucose genistein OH H
Of these isoflavone compounds, daidzein is an aglycone of daidzin having its glucose as a glycosidic saccharide hydrolytically separated therefrom, and genistein is an aglycone of genistin having its glucose as a glycosidic saccharide hydrolytically separated therefrom. With respect to the isoflavone compounds, contents thereof and percentages between daidzin and daidzein and between genistin and genistein in a defatted soybean are shown in the following Table 1.
TABLE 1 daidzin daidzein genistin genistein defatted 100 3.2 180 4.2 soybean (96.9%) (3.1%) (97.7%) (2.3&) (unit: mg/100 g)
It is understood from Table 1 that, in soybeans, daidzin and genistin are contained in large amounts while daidzein and genistein which are aglycones thereof are contained in smaller amounts.
On the other hand, it has been reported that a glycosidic saccharide is hydrolyzed from an isoflavone compound contained in soybeans to form an aglycone in the course of soy sauce or miso (fermented soybean paste) preparation [see Kihara, K.: Journal of Japan Soy Sauce Research Institute (for SHO-KEN), 16, 5, 190(1990)].
According to this report, although hydrolysis of a glycosidic saccharide proceeds to some extent in cooking of a defatted soybean or in a koji preparation step (seigiku step), most of the saccharide has already hydrolytically been separated in soy sauce cake or a soybean miso. However, since these are highly salinized, ingesting these in large quantities should be avoided. Accordingly, it is difficult to employ any process for preparing these as a process for preparing a food from a pulse crop as a starting material.
Soyasaponins occur in soybeans. For example, in a defatted soybean, soyasaponins occur in an amount of 500 to 700 mg/100 g. It has been reported that soyasaponins consist of 5 varieties of saponins, i.e., soya saponin I, soya saponin II, soya saponin III, soya saponin A1 and soya saponin A2 in the form of a mixture [see Kitagawa et al.: YAKUGAKU ZASSHI, 104, 2, 162-168(1984)]. Each of these has glucuronic acid as a glycosidic saccharide, and the aglycone which is such a compound that the glycosidic saccharide is removed therefrom includes two varieties of soyasapogenol A and soyasapogenol B. In general, however, the aglycone is present as soyasapogenol B. In a commercially available soybean miso, however, neither soyasapogenol A nor soyasapogenol B was detected.
Further, many reports have been made on pharmacological activities of various constituents contained in pulse crops.
For example, a Pueraria lobata Ohwi (kudzu), which is a type of legume, has been used for a long time as a material for an infusion of Pueraria root (Puerariae Radix) as an herb medicine. It has been reported that isoflavone compounds and saponins contained in Pueraria root have liver function improving effects (therapeutic activities against hepatopathy) [see "Nohara et al.: Journal of Medical and Pharmaceutical Society (for WAKAN-YAKU),. 5, 408-409(1988", "Y. Niiho et al.: YAKUGAKU ZASSHI., 109, 6, 424-431(1989)" and "Y. Niiho et al.: YAKUGAKU ZASSHI., 110, 8, 601-611(1990)"]. More specifically, an alcohol concentration, an acetaldehyde concentration and a concentration of ketones in blood can be lowered to prevent hangovers, nasty aftereffects of drinking or the like, and metabolic dysfunction of the liver can be prevented. Further, it has been reported that soyasaponins contained in soybeans have an anti-inflammatory effect, and can reduce serum cholesterol, neutral fats and phospholipids (cardiac function improving, lipotropic, antidiabetic, antifat, and flesh reducing effects) as well as the above-described effect in common with pueraria root [see Ohminami et al.: EIYO TO SHOKURYO., 34, 2, 105-108(1981)]. It is said that although soyasaponins have the effect of improving functions of a living body as described above, soyasaponins in the form of a glycoside can not be absorbed in a body. Accordingly, saponins in the form of a glycoside are not intestinally absorbable until they are decomposed into an aglycone, i.e., soyasapogenol B by enterobacteria having .beta.-glucuronidase effect. It is said that the decomposition takes a lot of time and thus the aglycone has little chance of being absorbed by a small intestine to lead to an extremely low absorption efficiency. On the other hand, the enterobacteria having .beta.-glucuronidase effect is not regarded as useful enterobacteria. Accordingly, placing no reliance on the decomposition by the enterobacteria, it is desired that soyasaponins be preliminarily decomposed in vitro into soyasapogenol B to ingest the latter. The same desire is true of the soy isoflavone compounds.
Further, soyasapogenol B is a triterpene compound and effective as an endotherine (ET) converter enzyme inhibitor (see Japanese Patent Application Laid-Open (Kokai) No. H7(1995)-188033) and inhibits an endotherine converter enzyme from exhibiting its function, and hence soyasapogenol B is effective as a remedy for endotherine (ET)-related disorders such as hypertension, cerebrovascular contraction after subarachnoid hemorrhage, myocardial infarction, arteriosclerosis, heart failure, renal failure, asthma, and so forth. Further, the triterpene compound has a lipase inhibitory effect and a glycerophosphate dehydrogenase inhibitory effect. Accordingly, the triterpene compound is capable of inhibiting the decomposition of lipids to prevent the lipids from being absorbed in a body, and thus, it is effective for the prevention and treatment of obesity (see Japanese Patent Application Laid-Open (Kokai) Nos. H9(1997)-40689 and H9(1997)-67249) and expected to improve cardial functions and to reduce flesh. Therefore, it is desired that soyasaponins be decomposed to obtain soyasapogenol B as an aglycone of saponins.
Moreover, it has been reported that free myo-inositol and the like, which are formed by the decomposition of phytic acid in soybeans, have a liver function improving effect of facilitating lipometabolism in a liver (therapeutic activities against hepatopathy) (see Kubota, H.: FOOD CHEMICAL, 8, 83-89 (1987).
A further description will be made on promotiing liver functions. It has been reported that miso soup has an anti-cancer effect, and this is because the enzyme activity of a liver is enhanced by the ingestion of miso soup [see Kanke, S.: SHOKU NO KAGAKU, 224, 50-54(1996)]. More specifically, it is reported that when iron as a carcinogen and oxidant and miso are fed to a rat or mouse, glutathione-s-transferase (GST) activity is increased. GST has been known to combine a carcinogen with glutathione to form a glutathione conjugate, which is excreted from a body. It is said that phase II xenobiotic-metabolizing enzymes to enhance carcinogen detoxication and elimination such as NAD(P)H: quinone oxidoreductase (DT diaphorase) and aldehyde dehydrogenase, as well as conjugating enzymes such as GST and UDP-glucuronosyl-transferase.
Accordingly, many proposals concerning isoflavone compounds contained in soybeans are disclosed in Japanese Patent Application Laid-Open (Kokai) Nos. S62(1987)-126186, H1(1989)-258669, H5(1993)-170756, and so on.